This invention relates to a contact device for making connection to an electronic circuit device and to methods of fabricating and using such a contact device, such as in the manufacture of semiconductor or other devices.
An important aspect of the manufacture of integrated circuit chips is the testing of the circuit embodied in the chip in order to verify that it operates according to specifications. Although the circuit could be tested after the chip has been packaged, the expense involved in dicing the wafer and packaging the individual chips makes it preferable to test the circuit as early as possible in the fabrication process, so that unnecessary efforts will not be expended on faulty devices. It is therefore desirable that the circuits be tested either immediately after wafer fabrication is completed, and before separation into dice, or after dicing, but before packaging. In either case, it is necessary to make electrical connection to the circuits"" external connection points (usually bonding pads) in a non-destructive way, so as not to interfere with subsequent packaging and connection operations.
U.S. Pat. No. 5,221,895 discloses a probe for testing integrated circuits. The probe includes a stiff metal substrate made of beryllium copper alloy, for example. The substrate is generally triangular in form and has two edges that converge from a support area toward a generally rectangular tip area. There is a layer of polyimide over one main face of the substrate, and gold conductor runs are formed over the layer of polyimide. The conductor runs and the metal substrate form microstrip transmission lines. The conductor runs extend parallel to one another over the tip area and fan out toward the support area. A contact bump is deposited on the end of each conductor run that is on the tip area. The tip area of the substrate is slit between each two adjacent conductor runs whereby the tip area is divided into multiple separately flexible fingers that project in cantilever fashion from the major portion of the substrate.
The probe shown in U.S. Pat. No. 5,221,895, is designed to be used in a test station. Such a test station may include four probes having the configuration shown in U.S. Pat. No. 5,221,895, the probes being arranged in an approximately horizontal orientation with their contact bumps facing downwards, with the four rows of contact bumps along four edges of a rectangle. The DUT is generally rectangular and has connection pads along the edges of one face. The DUT is placed in a vacuum chuck with its connection pads upwards. The vacuum chuck drives the DUT upward into contact with the probe, and overdrives the DUT by a predetermined distance from first contact. According to current industry standards, such a test station is designed to produce a nominal contact force of 10 grams at each connection pad. Therefore, the amount of the overdrive is calculated to be such that if contact is made at all connection pads simultaneously, so that each contact bump is deflected by the same amount, the total contact force will be 10 grams force multiplied by the number of connection pads.
If the material of the probe substrate is a beryllium copper alloy and each flexible finger has a length of about 0.75 mm, a width of about 62 microns and a height of about 250 microns, and the probe is supported so that the mechanical ground is at the root of the fingers, the contact force produced at the tip of the finger is about 7.7 grams for each micrometer of deflection of the tip of the finger. Therefore, if the contact bumps at the tips of the fingers are coplanar and the connection pads of the DUT are coplanar, and the plane of the contact bumps is parallel to the plane of the connection pads, an overdrive of about 1.3 microns from first contact will result in the desired contact force of 10 grams at each connection pad. However, if one of the connection pads should be 1.3 microns farther from the plane of the contact bumps than the other connection pads, when the DUT is displaced by 1.3 microns from first contact, there will be no contact force between this connection pad and its contact bump, and all the contact force that is generated will be consumed by the other contacts. If one assumes that the contact force at a connection pad must be at least 50 percent of the nominal contact force in order for there to be a reliable connection, then the maximum variance from the nominal height that this design will accommodate is xc2x10.7 microns. However, the height variations of contact bumps and connection pads produced by the standard processes currently employed in the semiconductor industry typically exceed 5 microns.
Furthermore, even if the contact bumps are coplanar and the connection pads are coplanar, tolerances in the probing apparatus make it impossible to ensure that the plane of the connection pads is parallel to the plane of the contact bumps, and, in order to accommodate these tolerances, it is necessary to displace the DUT by 75 microns in order to ensure contact at all connection pads. If the dimensions of the finger were changed to accommodate a displacement of 70-80 microns (75 micronsxc2x15 microns), the probe would become much less robust. If the probe were supported at a location further back from the root of the fingers, such that most of the deflection would be carried by the substrate rather than the fingers, the ability of the fingers to conform would be limited to 0.13 microns/gram deflection produced at the fingers themselves.
The connection pads of the DUT are not coplanar, nor are the connection bumps on the probe. Assuming that the nominal plane of the connection pads (the plane for which the sum of the squares of the distances of the pads from the plane is a minimum) is parallel with the nominal plane of the contact bumps, the variation in distance between the connection pad and the corresponding contact bump is up to 5 microns if both the DUT and the probe are of good quality.
At present, the connection points on an integrated circuit chip are at a pitch of at least 150 microns, but it is expected that it will be feasible for the pitch to be reduced to about 100 microns within a few years.
As the need arises to make connection at ever finer pitches, the stress in a probe of the kind shown in U.S. Pat. No. 5,221,895 increases. If the connection pads are at a spacing of 75 microns, this implies that the width of the fingers must be less than about 50 microns, and in order to keep the stress below the yield point, the height of the fingers must be at least 400 microns.
The necessary height of the fingers can be reduced by employing a metal of which the yield point is higher than that of beryllium copper. For example, if the substrate is made of stainless steel, having an elastic modulus of 207xc3x97109 N/m2, the maximum height of the fingers can be reduced to about 350 microns. However, it follows that the deflection is reduced below that necessary to comply with typical height variations found in the industry. Additionally, the resistivity of stainless steel is substantially higher than that of beryllium copper, and this limits the frequency of the signals that can be propagated by the microstrip transmission lines without unacceptable degradation. In general, prior techniques found limited application due to difficulties in achieving adequate deflection with the necessary force to achieve reliable connection, while withstanding the generated stresses.
In addition, although the microstrip transmission line has adequate characteristics for signals up to a frequency of 5 GHz, and it has been discovered that the so-called stripline configuration is desirable for higher frequencies.
In accordance with a first aspect of the present invention there is provided a method of making a multilayer composite structure for use in manufacture of a contact device for establishing electrical connection to a circuit device, said method comprising providing a substrate of a metal having a resistivity substantially greater than about 10 micro-ohm cm, adhering a first layer of metal having a resistivity less than about 3 micro-ohm cm to a main face of the substrate, the first layer having a main face that is remote from the substrate, adhering a second layer of dielectric material to the main face of the first layer, the second layer having a main face that is remote from the substrate, and adhering a third layer of metal to the main face of the second layer, the metal of the third layer having a resistivity less than abut 3 micro-ohm cm.
In accordance with a second aspect of the present invention there is provided a method of making a contact device for use in establishing electrical connection to a circuit device, said method comprising providing a substrate of a metal having a resistivity substantially greater than about 10 micro-ohm cm, the substrate having a major portion and a tip portion projecting therefrom along an axis, adhering a first layer of metal having a resistivity less than about 3 micro-ohm cm to a main face of the substrate, the first layer having a main face that is remote from the substrate, adhering a second layer of dielectric material to the main face of the first layer, the second layer having a main face that is remote from the substrate, adhering a third layer of metal to the main face of the second layer, the metal of the third layer having a resistivity less than about 3 micro-ohm cm, selectively removing metal of the third layer to form discrete conductor runs extending over the tip portion parallel to said axis, while leaving portions of the second layer exposed between the conductor runs, whereby a multi-layer composite structure is formed, and slitting the tip portion of the composite structure parallel to said axis, whereby fingers are formed that project from the major portion of the composite structure in cantilever fashion and each of which supports at least one conductor run.
In accordance with a third aspect of the present invention there is provided a probe apparatus for use in testing an integrated circuit embodied in an integrated circuit chip, said probe apparatus comprising a support member having a generally planar datum surface, a generally planar elastic probe member having a proximal end and a distal end, at least one attachment member attaching the probe member at its proximal end to the support member with the probe member in contact with the datum surface, at least one adjustment member effective between the support member and a location on the probe member that is between the proximal and distal ends thereof for urging the distal end of the probe member away from the support member, whereby the probe member undergoes elastic deflection.
In accordance with a fourth aspect of the present invention there is provided a probe apparatus for use in testing an integrated circuit embodied in an integrated circuit chip, said probe apparatus comprising a support member having a bearing surface, a probe member having a proximal end and a distal end and comprising a stiff substrate having first and second opposite main faces and conductor runs extending over the first main face of the substrate from the distal end of the substrate to the proximal end thereof, the conductor runs of the probe member being distributed over a connection region of the first main face of the substrate in a first predetermined pattern, at least one attachment member attaching the probe member to the support member with the second main face of the probe member confronting the bearing surface of the support member, a circuit board comprising a substrate having a main face and conductor runs distributed over a connection region of said main face of the circuit board in a second predetermined pattern, a flexible circuit comprising a flexible substrate having a main face and first and second connection regions, and conductor runs extending between the first and second connection regions of the flexible substrate and distributed over the first connection region in a pattern corresponding to said first pattern and distributed over the second connection region in a pattern corresponding to said second pattern, a first attachment device attaching the flexible circuit to the support member with the first connection region of the flexible circuit confronting the connection region of the probe member and the conductor runs of the flexible circuit in electrically conductive connection with respective conductor runs of the probe member, and a second attachment device attaching the flexible circuit to the circuit board with the second connection region of the flexible circuit confronting the connection region of the circuit board and the conductor runs of the flexible circuit in electrically conductive connection with respective conductor runs of the circuit board.
In accordance with a fifth aspect of the present invention there is provided a method of making a multilayer composite structure for use in manufacture of a contact device for establishing electrical connection to a circuit device, said method comprising providing a substrate, adhering a first layer of dielectric material to a main face of the substrate, the first layer having a main face that is remote from the substrate, and adhering a second layer of metal to the main face of the first layer, the metal of the second layer having a resistivity less than about 3 micro-ohm cm.
In accordance with a sixth aspect of the present invention there is provided a method of making a contact device for use in establishing electrical connection to a circuit device, said method comprising providing a substrate having a major portion and a tip portion projecting therefrom along an axis, adhering a first layer of dielectric material to the main face of the substrate, the first layer having a main face that is remote from the substrate, adhering a second layer of metal to the main face of the first layer, the metal of the second layer having a resistivity less than about 3 micro-ohm cm, selectively removing metal of the second layer to form discrete conductor runs extending over the tip portion parallel to said axis, while leaving portions of the first layer exposed between the conductor runs, whereby a multilayer composite structure is formed, and slitting the tip portion of the composite structure parallel to said axis, whereby fingers are formed that project from the major portion of the composite structure in cantilever fashion and each of which supports at least one conductor run.
In accordance with a seventh aspect of the present invention there is provided a contact device having a plurality of nominally coplanar first contact elements for making electrical contact with corresponding nominally coplanar second contact elements of an electronic device by positioning the contact device and the electronic device so that the plane of the first contact elements is substantially parallel to the plane of the second contact elements and effecting relative displacement of the devices in a direction substantially perpendicular to the plane of the first contact elements and the plane of the second contact elements to generate a contact force of at least f at each pair of corresponding first and second contact elements, wherein it is necessary to effect relative displacement of the devices by a distance d in said direction from first touchdown to last touchdown, said contact device comprising a stiff substrate having a major portion with fingers projecting therefrom in cantilever fashion, each finger having a proximal end at which it is connected to the major portion of the substrate and an opposite distal end and there being at least one, and no more than two, contact elements on the distal end of each finger, a support member to which the substrate is attached in a manner such that on applying force in said direction to the distal ends of the fingers, deflection occurs both in the fingers and in the major portion of the substrate, and means for effecting relative movement of the devices in said direction, and wherein the substrate is dimensioned such that relative displacement of the devices in said direction by a distance d from first touchdown generates a reaction force at each contact element of about 0.1*fxc2x10.1*f, and further relative displacement of the devices in said direction by a distance of about 75 micron or 5*d beyond last touchdown generates a reaction force at each contact element of about 0.9*fxc2x10.1*f.
In accordance with an eight aspect of the present invention, there is provided a method for testing/manufacturing devices such as integrated circuits or displays (such as LCD panels), which may include the steps of carrying out a manufacturing process for the DUT, such as a planar-type integrated circuit manufacturing process, positioning the DUT on a positioning device, such as a vacuum chuck (the DUT may be in wafer or die form, in the case of integrated circuits, etc.), effecting alignment of a contact device in accordance with the present invention with the DUT to the extent required for proper placement, effecting relative movement of the DUT with respect to the contact device to establish initial contact thereto (as determined electrically or by a mechanical means), over-driving the relative movement to establish reliable electrical connection, wherein stresses are desirably shared between the extended fingers of the contact device and the substrate of the contact device, applying test signals to the DUT and determining whether the DUT is defective or otherwise within or outside acceptable specifications, recording whether the pass/fail condition of the DUT (which may include mechanical notation, such as inking the DUT if defective, etc., or by data recording), removing the DUT from the positioning device, and packaging and assembling the DUT if acceptable.
With the present invention, devices with connection points of fine pitch may be reliably tested and manufactured.